diff --git a/src/hdf5_lib.py b/src/hdf5_lib.py
index 07e12ce..7c498a1 100644
--- a/src/hdf5_lib.py
+++ b/src/hdf5_lib.py
@@ -495,7 +495,7 @@ def save_processed_dataframe_to_hdf5(df, annotator, src_hdf5_path, script_date,
     """
     # Convert datetime columns to string
     datetime_cols = df.select_dtypes(include=['datetime64']).columns
-    df[datetime_cols] = df[datetime_cols].applymap(str)
+    df[datetime_cols] = df[datetime_cols].apply(str)
 
     # Convert dataframe to structured array
     icad_data_table = utils.dataframe_to_np_structured_array(df)